IEEE 1394 cable connector with short circuit switch

ABSTRACT

In case of a loss of power supply a short-circuit between the corresponding pins of the two IEEE 1394 connectors of a device is established. Preferably this will be achieved by a relay controlling switches. If power is available, the relay is powered and the switches are open. The device then behaves like without this extension. If power is lost, the relay is not powered any longer, and the switches are closed. By this way, the device simply disappears from the cluster, which will then be reorganised according to IEEE 1394 rules.

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/EP00/04693, filed May 23, 2000, which waspublished in accordance with PCT Article 21(2) on Dec. 14, 2000 inEnglish and which claims the benefit of European patent application No.99110705.3 filed Jun. 3, 1999.

The invention relates to an IEEE 1394 cable connector.

BACKGROUND

The IEEE 1394 standard describes a high speed, low cost Serial Bussuitable for use as a peripheral bus or a backup to parallel back-planebuses. Highlights of the Serial Bus include:

a) Automatic assignment of node addresses—no need for address switches.

b) Variable speed data transmission based on ISDN-compatible 1 bit ratesfrom 24.576 Mbit/s for TTL backplanes to 49.152 Mbit/s for BTLbackplanes to 98.304, 196.608, and 393.216 Mbit/s for the cable medium.

c) The cable medium allows up to 16 physical connections (cable hops)each of up to 4.5 meters, giving a total cable distance of 72 metersbetween any two devices. Bus management recognises smallerconfigurations to optimise performance.

d) Bus transactions that include both block and single quadlet reads andwrites, as well as an “isochronous” mode which provides a low-overheadguaranteed bandwidth service.

e) A physical layer (PHY) supporting both cable media and backplanebusses.

f) A fair bus access mechanism that guarantees all nodes equal access.The backplane environment adds a priority mechanism, but one thatensures that nodes using the fair protocol are still guaranteed at leastpartial access.

An IEEE 1394 4-pin cable connects a pair of devices, a further devicecan be added by another cable attached to one of the former two,etc.—thus establishing a cluster or chain of devices. This chaincontains devices which have two neighbouring devices attached to them,as well as devices at the end of the chain with only one neighbour. Eachdevice has a mains connection, and when the device is switched off andgoes into a stand-by mode, its IEEE 1394 physical layer implementationis still powered to provide certain functionality. If for example thehome user disconnects the power plug of one device in a chain—e.g., theTV set—this stand-by function will be lost. As a consequence, the PHYlayer functionality is lost and the chain is broken—leaving two separatesmaller clusters of devices.

In order to avoid a break of the chain in case of internal power supplyfailure a solution is described in the IEEE 1394 standard, using a powerstorage device to provide power to the devices, while these devices aregracefully shutting down after the internal power supply fails. Normallythe internal power supply provides power for the PHY and the powerstorage device. If the internal power supply fails a power fail senseline signals the logic that a failure has occurred and the load switchesover to the power storage device.

INVENTION

It is an object of the present invention to disclose an IEEE 1394 cableconnector, that allows bus connections to all available devices linkedto the bus in case of power failure of one device.

According to the invention, this object is achieved by means of thefeatures specified in main claims. Advantageous designs and developmentsare specified in subclaims.

In case of a loss of power supply a short-circuit between thecorresponding pins of the two IEEE 1394 connectors of a device isestablished. Preferably this will be achieved by a relay controllingswitches. If power is available, the relay is powered and the switchesare open. The device then behaves like without this extension. If poweris lost, the relay is not powered any longer, and the switches areclosed. By this way, the device simply disappears from the cluster,which will then be reorganised according to IEEE 1394 rules.

DRAWINGS

Embodiments of the invention are described with reference to theaccompanying drawing, which shows in:

FIG. 1a Bus connection implementation in power available case;

FIG. 1b Bus connection implementation in power lost case;

EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention are explained in more detail inthe following description.

FIG. 1 shows an example of a bus connection implementation in poweravailable case. A relay 1 controlling four switches 2 with contacts a,b, c, d is connected with the regular power supply already available inthe respective device via a resistor R_(v). All switches 2 are connectedwith the 4 respective pins of the two IEEE 1394 connectors 3, 4available in the device in the way shown in FIG. 1a. FIG. 1a shows theswitch position of the relay 1 in the case of power being available tothe device. In this case there is no short-circuit established betweencorresponding pins of the two IEEE 1394 connectors.

FIG. 1b shows the case where the mains connection of the device has beenlost and power is not available. The relay 1 turns into its restingposition closing the contacts a, b, c, d of the four switches 2. In thisposition the 4 respective pins of the two IEEE 1394 connectors 3, 4 areconnected. By this way, the two IEEE 1394 cables attached to the deviceat these connectors 3, 4 are transformed into a new, longer cable. Thepowerless device disappears from the cluster it has formed part ofbefore. The cluster will now be reorganized with one device less, andwill stay operational.

If a device equipped with the invention is disconnected from the mains,e.g. a TV set, the cluster it has formed part of will still beoperational.

Since the two cables attached to the device form one new longer cablenow, the “new” cable should not exceed the longest cable length thatstill allows IEEE 1394 operation in the given situation. The inventionhelps in all cases where this length is not exceeded. Without theinvention, the cluster would be broken at the point of the disconnecteddevice.

Instead of a relay with switches also electronic switches can be used.

What is claimed is:
 1. Device having a power supply and at least twoIEEE 1394 cable connectors with pins for data lines or data lines andadditional power supply lines, wherein, short-circuit switches areprovided that are adapted to connect together the data line pins of onecable connector with corresponding data line pins of the other cableconnector via short-circuit switches, the device comprising means foropening the short-circuit switches in case the device is powered bymeans of the power supply, and for closing the short-circuit switches incase the power supply stops providing power to the device, therebymaintaining data throughput from one cable connector to the other cableconnector in case of a power loss.
 2. Device according to claim 1,wherein the short-circuit switches are part of a relay.
 3. Deviceaccording to claim 1, wherein the short-circuit switches are designed aselectronic switches.